1. Field of the Invention
The invention relates to an implantable heart stimulator for the cardiac resynchronization therapy (CRT) of a heart. The heart stimulator may be a cardiac pacemaker or an implantable cardioverter/defibrillator (ICD) or a combination of both, which is capable of stimulating one or both atria and one or both ventricles.
2. Description of the Related Art
A heart stimulator of this type typically has one sensing unit and one stimulation unit in each case for all cardiac atria and ventricles included in its function. These units are each connected via electrode lines to electrodes to be implanted at suitable points in the heart in operation of the heart stimulator. The electrode line having the electrodes for detecting electrical potentials in the right atrium of the heart and for delivering right-atrial stimulation pulses are typically components of an atrial electrode line, for example. The electrodes for detecting electrical potentials in the right ventricle and for delivering right-ventricular stimulation pulses are typically fastened to a right-ventricular electrode line, whose distal end extends up into the apex of the right ventricle. The electrode line having the electrodes for detecting electrical potentials in the left ventricle of the heart and for delivering left-ventricular stimulation pulses is typically a component of a left-ventricular electrode line, which is laid through the coronary sinus of a heart and therefore is also referred to as a coronary sinus electrode line. All electrode lines are typically connected at their proximal end via standardized plug connections to a corresponding heart stimulator.
The typical stimulation modes of a heart stimulator, such as AAI, VVI, VDD, or DDD may be assumed to be known. This is also true for the delivery of stimulation pulses only as needed (demand pacemaker), in which the delivery of a stimulation pulse to the atrium or to the particular ventricles of a heart is suppressed if a particular intrinsic action (intrinsic contraction) of the heart atrium or the heart ventricle was previously detected via an assigned sensing unit of the heart stimulator in a corresponding escape interval. These concepts, which are known per se, may also be implemented in the heart stimulator described here.
For an atrium-synchronous stimulation, in particular in a biventricular DDD stimulation mode, an atrioventricular delay interval (also referred to hereafter as the atrioventricular delay time or as the AV time) which is adapted as well as possible to the individual patients is desirable. The atrioventricular delay time begins with an atrial trigger event and ends with a stimulation of the ventricle. The atrial trigger event may, depending on the current stimulation mode (VDD or DDD stimulation), either be the natural atrial action perceived via an atrial electrode or an atrial stimulus. The atrioventricular delay times are thus determined by two different time intervals, either that for the DDD stimulation or that for the VDD stimulation being active as a function of the current stimulation mode of the pacemaker.
The interatrial conduction time begins in DDD stimulation with the right-atrial stimulus and in DDD stimulation with a signal feature characterizing the right-atrial contraction, and ends in both stimulation modes with an electrical signal feature which characterizes the left-atrial contraction.
The stimulation of the ventricle (ventricular stimulation) typically results in a contraction of the stimulated ventricle, i.e., in a stimulated ventricular event. A ventricular contraction does not occur after ventricular stimulation only if the ventricular is still refractory because of a corresponding contraction occurring shortly beforehand or if the strength of the ventricular stimulation pulse is insufficient (is sub-threshold) to depolarize at least some cells of the ventricular myocardium. A ventricular stimulation pulse is also not even triggered in the so-called demand mode of the heart stimulator if the cardiac pacemaker detects a natural ventricular contraction (a natural ventricular event) within a ventricular escape interval, which is a function of the atrioventricular delay time. In this case, the delivery of the ventricular stimulation pulse is inhibited. All of these may be presumed to be known.
The detection of a contraction is typically performed with the aid of electrodes which record electrical potentials of the myocardium in the particular cardiac area (this refers to the particular atrium or the particular ventricle of a heart) and by a particular sensing unit which analyzes the particular time curve of the recorded potential, and in the simplest case by a threshold value comparison. This is because the potential curve displays typical signal peaks in the case of depolarizations of the myocardium accompanying a contraction of the myocardium in the particular cardiac area.